A device under test (DUT), such as an integrated circuit (IC) is typically tested in a controlled environment prior to its production. Test results are oftentimes recorded, and an analysis of the recorded results provides a basis for predicting the device's failure point at varying operational parameters, e.g., operational voltage, frequency, or temperature. Commonly, test results are recorded in a two-dimensional plot, e.g., a “shmoo plot.”
A shmoo plot generally exhibits the results of tests performed of a DUT's resources across defined ranges of the aforementioned operational parameters. For example, the horizontal axis of a shmoo plot might define a range of operational voltages between 1.00 volts and 1.60 volts at increments of 0.05, and the vertical axis of the shmoo plot might define a range of internal clock frequencies between 900 and 1200 hertz at increments of 15 Hertz. Moreover, for each intersection point on the shmoo plot, a voltage/frequency pair is applied to the DUT, and whether the DUT passes or fails is recorded in the shmoo plot.
A system for testing a DUT in this manner usually comprises automated test equipment (ATE) that interfaces with the DUT and that is capable of automatically varying the DUT's operational and/or environmental parameters. Oftentimes, the ATE also interfaces with a control element, e.g., a computer, that controls the ATE and records the test results. Usually, the test results comprise pass/fail data indicative of whether the DUT passed or failed, and this data is collected via the ATE. Sometimes the control element records this data in a shmoo plot, as described herein.
The recorded test results exhibited in a shmoo plot reveal the operational behavior of the DUT in that the shape of a failing region of a shmoo plot is meaningful and helps to determine the cause of a failure in the DUT. The shape of a shmoo plot typically falls into familiar categories that are recognized by descriptive names, depending upon the shape that the data takes when plotted. For example, a shmoo plot of a normal circuit operation usually shows better high frequency performance as supply voltage increases, and as such its shape resembles a “shmoo,” which is a mid-twentieth century Lil'Abner cartoon character. However, the shmoo plot may take various identifying forms depending upon the type of failure, if any, that is exhibited by the DUT.
Testing of a DUT at varying operational parameters usurps extensive time and resources in light of the procedures used to obtain sufficient data for defining a shmoo plot. In this regard, if a shmoo plot comprises, for example, ten (10) operational voltages in the horizontal axis and ten (10) internal clock frequencies in the vertical axis, then obtaining a complete shmoo plot for the DUT would require that one hundred tests be run and recorded. Thus, testing a DUT and recording values indicative of the test results slows the research, development and manufacturing process of ICs.